About the Watch Charts

These radial charts visualize every hour (or day) when a set of weather and ocean conditions all align at once. Each concentric ring tracks one condition across the calendar year. The highlighted arcs show where every condition was simultaneously met — the actual windows for surfing or skiing.

Nahant Surf Windows

Seven conditions must align for a viable surf session at Nahant Beach, north of Boston. The chart checks each hour of the year:

1. Low tide ±1 hour — NOAA tide predictions for station 8443970
2. Swell ≥ 2 ft — Open-Meteo Marine swell wave height
3. Offshore or light wind — wind from 210–330° or ≤ 6 knots
4. Daylight — between sunrise and sunset
5. No precipitation — zero hourly rainfall
6. Air > 40°F — 2m air temperature
7. Water > 45°F — sea surface temperature

Explore the interactive surf chart →

Cannon Mountain Powder Days

Three conditions are checked at 9 AM each day for Cannon Mountain in Franconia Notch, NH:

1. Fresh snow (48h rolling ≥ 8 cm) — ERA5 hourly snowfall, summed over a 48-hour window. ERA5 underestimates mountain snowfall at its ~31 km grid, so 8 cm is a calibrated proxy for roughly 6″+ of real snow.
2. Deep base (≥ 0.40 m) — ERA5-Land snow depth at ~9 km resolution, better suited for mountain terrain. 0.40 m approximates an established skiable base.
3. Air > 0°F — 2m air temperature at 9 AM. Too cold and lifts may close or conditions become dangerous.

Explore the interactive powder chart →